Passive optical networks enable a plurality of optoelectronic transceivers to share one or more optical fibers while transmitting and receiving data in an optical form. Typically, passive optical networks employ a time division multiplexing access (TDMA) scheme to make this possible. In such schemes, the data transmission capabilities of the plurality of optoelectronic transceivers are operational only during separate, non-overlapping periods of time.
When the turn-on and turn-off times of the optoelectronic transceivers decrease, the amount of time available to each optoelectronic transceiver in a passive optical network to transmit optical data increases. Prior art optoelectronic transceivers are able to turn a laser diode on and off within 100 microseconds to 1 millisecond.
Persons skilled in the art, moreover, recognize that turning a laser diode on and off is a time consuming aspect of turning an optoelectronic transceiver on and off. Passive optical networks, therefore, require laser diodes to be turned on and off quickly to make efficient use of network bandwidth.
A laser diode is typically embedded in a feedback loop of an optoelectronic transceiver. This feedback loop turns the laser diode on, and then maintains the laser diode in a linear operating range so that it is able to transmit data efficiently. Maintaining the operational efficiency of the laser diode includes adjustments to the output of an operational amplifier, which is a portion of the feedback loop. Persons skilled in the art recognize that the optical output power of a given laser diode may fluctuate in ways that are inconsistent with electrical input that is intended to modulate the optical output of the laser diode. The purpose of the feedback loop is to counteract these unwanted fluctuations.
In particular, the operational amplifier produces a bias current to maintain the operational efficiency of the laser diode. However, feedback loops (e.g., operational amplifiers) with a large bandwidth tend to null out the electrical input that is intended to modulate the optical output of a corresponding laser diode. This is so because the bandwidth of a feedback loop may overlap some or all of the bandwidth of the electrical input. This is problematic in the context of passive optical networks because feedback loops with a large bandwidth are ideal for turning a laser diode on and off quickly (and thus enable optoelectronic transceivers in a passive optical network to transmit more optical data or the inclusion of additional optoelectronic transceivers in the passive optical network). More specifically, feedback loops with a large bandwidth are able to modulate the optical output strength of a given laser diode at a relatively high frequency.
What is needed in the art, therefore, is an optoelectronic transceiver capable of turning a laser diode on and off within 0.1 to 1.0 microseconds that does not adversely affect electrical input.